As described in the aforementioned patent applications, vapor is generated starting from an induction-heated pot. The injected energy from which the losses are taken corresponds to the molar evaporation volume. The correlation is completely linear.
This vapor generator must be supplied with metal so as to compensate for the evaporated volumes. After having examined different supply modes, a supply with liquid metal was selected. On a continuous industrial line, the supply must in fact be automatic. On a steel line for coating using magnesium or zinc, the strip deposition involves hundreds of kg, or even tons of metal per hour. The supply of the pot may not be directly in solid form (cord, granulates, ingots, etc.), as that would for example require the use of an airlock system with vacuum compartments, which is too complex. In the present technology, the pot is supplied with liquid metal pumped into a pipe from a melting furnace located below the pot and at atmospheric pressure.
Furthermore, in the pot, only the species for which the obtained saturating vapor pressure enables evaporation will evaporate. The other species will remain in the pot and build up. This is a form of distillation. All of the impurities contained in the basic metal (which is not 100% pure for cost reasons) that are impossible or difficult to evaporate will thus build up in the pot. Their concentration will end up hindering, or even preventing evaporation. These impurities must therefore be eliminated periodically or continually.
Among the materials that may build up in the evaporation pot are in particular metal oxides of the basic metal. These oxides primarily come from the filling metal, which is generally purchased in ingots whereof the outer surface is oxidized. A digital simulation on an industrial prototype with a moderate evaporation capacity showed that the concentration level of impurities could reach 10%, after 40 hours of production and considering a basic material with a purity of 99.8% (magnesium). The oxides that are present may either decant or float due to their separation from the basic metal by segregation. In this second separation mode, they can greatly influence evaporation.
With vapor generators for this type of facility, the following problems or requirements therefore arise:                startup of the facility while the evaporation pot is empty;        prevention, during startup, in the event of a leak through a vapor distribution valve, of the evaporation of the metal in the pipe, toward the vacuum deposition head. These leaks are very harmful, as they cause static depositions on the strip in standby (in the form of beads). Furthermore, compensating the evaporation flow rate, and the large quantity of energy taken from the metal (latent evaporation heat), requires major additional power. To prevent cooling of the liquid metal, it would be necessary to install considerable power over the entire length of the liquid pipes, which is technically impossible given the power density per surface unit that would need to be installed;        startup of the melting furnace and prevention of metal evaporation under the effect of the vacuum;        preventing the formation of a solid plug on the free surface of the furnace and in the pipes, due to the evaporation and which would prevent the conversion to liquid form and the supply of the pot;        prevention of the solidification of the metal in the supply pipe, which would otherwise lead, during re-melting, to a break of the pipe under the effect of the metal expansion;        emptying of the pipes containing the liquid so as to be able to avoid the previous issue and to be able to disassemble the pipes for the maintenance thereof;        startup of the melting furnace, which requires more than 10 hours of heating, without having to heat the entire remainder of the facility or to create the vacuum. In fact, the heating necessary for the remainder of the facility to avoid condensation of the vapors on the cold wall is much shorter (e.g., 2 hours);        allowing to solidify in the pipes without breaking them.        